Imaging systems, such as printers, facsimile machines, and copiers, are very common today in the workplace and in homes. In the current business environment, imaging systems have become crucial to every day business activities. As such, the reliability and smooth operation of imaging systems is of paramount importance. It is, therefore, important to design imaging systems so that downtime and work interruptions are minimized. This can be a daunting challenge, given the complexity of systems in which sheet material must be received, moved through the imaging process, and distributed from the imaging system in a matter of seconds.
Many imaging systems have not only an imaging device, but are also equipped with media handling devices. Media handling devices perform such tasks as collating, organizing, stacking, and stapling media, or sheet material, as it is output from the imaging device. This is a very important function when handling large volumes of sheet material (e.g. paper products or other media). These devices are commonly physically joined to the imaging system.
One common function of a media handling device is to “flip” sheet material as it exits the imaging system. That is, the leading edge of a sheet material becomes the trailing edge as the media handling device “flips” a sheet material from face-up to face-down, or vice-versa. In most media handling devices this flipping operation is useful for accumulating print jobs properly in a “bin module” in order to collate and staple the sheet material. This flipping function is usually accomplished by a flipper module within the media handling device.
The flipper module generally begins its operation by accelerating a piece of sheet material as it exits the imaging system in order to generate a gap between adjacent pieces of sheet material. This gap gives the flipper module time to flip the accelerated sheet. This acceleration is usually accomplished by a shaft that exerts a force on a piece of sheet material through frictional rollers. The shaft and the rollers are usually driven by a stepper motor. While the use of a stepper motor in a flipper module is somewhat effective at accelerating a piece of sheet material to be “flipped,” there are several drawbacks to this approach.
It must be understood that it is important in media handling devices to control the speed of the sheet material and the torque placed upon the sheet material. If an excessive amount of torque is placed on a sheet material, the material may become damaged. Furthermore, excessive torque may lead to the generation of undesirable acoustic noise, depending on the weight of the sheet material. On the other hand, if the speed of the sheet material is not controlled properly, the leading edge of one sheet may run into the trailing edge of a preceding sheet. In either situation, there will likely be what is commonly known as a “media jam” of the paper handling device.
Speed and torque control is especially important in flipping operations. As noted above, a sheet entering the flipper module is typically first accelerated so as to separate it from a succeeding piece of sheet material. This acceleration gives the first sheet of material time to be flipped by the flipper module before the succeeding sheet of material enters the flipper module.
With a stepper motor, the motor, with feedback from an encoder system, is required to self-adjust, or perform a calibration routine for every sheet of material that enters the flipper module. This self-adjust feature is usually necessary to achieve proper torque control over the sheet. In a typical paper handling device, the self calibration routine requires approximately 150 milliseconds for every sheet, and about 1 second for a full calibration, which must be accomplished every specified number of sheets. The time spent in this calibration routine does not allow the paper handling device flipper module to receive another sheet immediately, simply because of the time required to run the calibration routine.
There are also characteristics of stepper motors, generally, that make stepper motors less than the most desirable solution for the driving motor in a flipper module. For example, stepper motors tend to cause vibrations which resonate with the paper handling device's frame. Additionally, if the media handling device ever stops, starting the stepper motor with paper in the rollers is very difficult. Such an occurrence is known as a “stepper stall” and is due generally to the non-linear nature of stepper motors.
Thus, a heretofore-unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies in paper handling devices.